1. Field of the Invention
The present invention relates to a photomagnetic data memorizing apparatus, e.g., a photomagnetic data memorizing disk apparatus capable of performing high-density data write.
2. Description of the Related Art
Conventionally, to write data on a photomagnetic disk, a laser beam is radiated on a magnetic film while a magnetic field is applied to the magnetic film, so that part of the film the temperature of which is increased to a predetermined value (Curie temperature) or more and which has thus lost its coercive force is magnetized, thereby forming a memory pit. To read data, a low-temperature laser beam necessary for data read is spot-radiated, and light reflected by the disk surface is read.
However, the size of a memory pit which can be read is limited by a detecting limit determined by a laser wavelength and a numerical aperture of a lens.
A photomagnetic disk in which the magnetic film has a two-layered structure is experimentally manufactured. One of the two layers is used as a mask to cover pits other than one memory pit from which data is to be read, so that data can be read from memory pits formed at a smaller pitch than the spot diameter of the read beam. In this case, the write wavelength is a short wavelength of less than half the conventional detection limit, and the resolution is increased to twice or more.
According to this technique, a temperature difference is present within a beam spot (Gaussian distribution) formed by beam radiation during reading, and pit reading is enabled only from a high-temperature area within the beam spot. Therefore, the same effect as that obtained when the read beam spot area (diameter) is decreased can be obtained accordingly, and high-density data write can be realized by using the optical system of an existing photomagnetic disk apparatus.
However, although high-density data write can be realized by using the existing laser optical system, no attempt has been so far made to put this idea in practical use, and associated techniques for further increasing the data write density are not sufficient.